The use of biorenewable components as substitutes, either in whole or in part, for petrochemical derived raw materials is an emerging trend in the chemical industry. At least one benefit includes the use of a raw material that is non-depleting of fossil resources (i.e., renewable), and in some cases a reduction in lifecycle global warming potential due to the fixation of CO2 in plant biomass from which the biorenewable materials are derived.
Biorenewable raw materials are typically either carbohydrate based or natural oil based. Prior to their end-use as polyols, the biorenewable raw material may or may not undergo further chemical transformation, with or without other petrochemical based materials.
There are challenges to the use of natural oils as raw materials for polyols to be used in isocyanate based foam products (e.g., polyurethanes and polyisocyanurates). The natural oils, with the exception of those oils having hydroxyl functionality (e.g. castor oil, or lesquerella oil), typically lack isocyanate reactive functionality, and must undergo chemical transformation, such as, for example, transesterification with functionalized materials, epoxidation and ring opening, oxidation, ozonolysis, or hydroformylation to add reactive functionality. The added reactive functionality could be any active hydrogen moiety, and is typically hydroxyl groups or amines.
The properties (e.g., compressive strength, green strength, reactivity, thermal stability) of resultant foams formed from the reaction of functionalized natural oils with isocyanate are often deteriorated relative to foams made solely from petrochemical polyols, aromatic polyester polyols in particular. This deterioration of foam properties can be due, at least in part, to the plasticization of the foam by the relatively high aliphatic concentration of the natural oils. The deterioration of foam properties can also be due, at least in part, to the poor reactivity of the functional group due to steric hindrance by the aliphatic chains of the oil, and the incompatibility of the natural oil polyol with the isocyanate. The deterioration of foam properties can also be due to the functionality reduction to the polyester polyol by the end capping action of fatty acids.
Also, when natural oils are used in combination with petrochemical polyols, the natural oil is frequently not compatible with the petrochemical polyol, which again results in the deterioration of foam properties. This is often the case with aromatic polyester polyols, and compatibility becomes an important issue for the end user who must blend and use (e.g., mix with an isocyanate) the polyol before its separation into component parts.
Polyester polyols are also utilized in polyurethane non-foam applications, such as in coatings, adhesives, sealants and elastomers (CASE) applications. Using biorenewable materials in polyester polyols for CASE applications presents the same challenges with respect to isocyanate reactivity and petrochemical compatibility as presented in polyurethane and polyisocyanurate foam applications. With elastomers, the loss of functionality can cause a loss of hysteresis, fatigue and creep properties. In the case of coatings, chain termination and subsequent loss of polymer network formation can result in a loss of toughness and durability.
There is still a need for polyester polyol compositions containing biorenewable components, which can be used to make polyurethane and polyisocyanurate foams, such as pentane blown foams, having good foam strength, flammability resistance and insulation characteristics. Desirably, these polyol compositions should maintain pentane compatibility, have a good reactivity profile, mix well with isocyanate, and minimally deteriorate the physical and thermal properties of the resultant foams. There is also a need for improved polyester polyol compositions containing biorenewable components which can be used in CASE applications and flexible foams.